With the purpose of verify the presence of larvae from the genus Gasterophilus in the Rio Grande do Sul State, a study was undertaken using 395 horses taken to slaughter in the city of Pelotas. The material analysis revealed that 126 animals (31,90%) presented infection, with 100 animals (25, infected by Gasterophilus nasalis, and 47 animals (11,90%) infected by G intestinalis. These results also represent the first report of the definite establishment of G intestinalis as a horse parasite in Brazil. The probable implications of G. intestinalis occurrence in Brazil are discussed.

The genus Gasterophilus (Díptera, Oestridae) includes eight species of flies whose larvae cause gastrointestinal myiasis in equids1. In Brazil Gasterophilus intestinalis De Geer, 17762 and Gasterophilus nasalis Linnaeus 17583 were the two species described until now.

The myiasis develops for a period of 10 to 12 months in different regions of the equine digestive tract4. G nasalis larvae of second and third instar (L2 and L3) are found in the pylorus and first portion of the duodenum, immediately after the pyloric sphincter5, whereas L2 and L3 larvae from G intestinalis are usually found in the non-glandular portion of the stomach.

Apart from the losses caused to equids, there are reports of infections caused by gasterophilids in dogs, pigs, birds7 and human beings8.

Studies on the occurrence and prevalence of the genus Gasterophilus undertaken in Brazil suggest just the presence of G Nasalis 915. The occurrence of G intestinalis has been reported, in isolated cases of imported animals216, and therefore the species is not yet considered as established in Brazil14.

The updating of the general occurrence and seasonal occurrence of the genus Gasterophilus in Brazil is important, not only to help the clinical diagnosis and control planning of gasterophilosis, but also from a biological and ecological point of view1.

This study reports the occurrence of gasterophilids in horses slaughtered at a slaughterhouse in Rio Grande do Sul State, and indicates the establishment of G. intestinalis in Brazil.

MATERIAL AND METHODS

The stomachs of 395 horses were analyzed after slaughter at a commercial slaughterhouse in the city of Pelotas, Rio Grade do Sul. The studied horses were from different regions of the State. The city of origin and the sex of each animal were registered, but no specification was made as to breed or age.

After the evisceration, the animals' stomachs were opened on the greater curvature, from the cardia to the pylorus, together with the first portion of the duodenum; these were examined in search for the larval forms of Gasterophilus spp. When found, the point of fixation (cardia, non-glandular region, glandular region, pilorum-duodenum) was registered and the sample was collected and stored individually. These samples were taken immediately to the laboratory, where they were weighed and identified by appropriate keys4 (Figure 1).

RESULTS

The findings on the slaughtered animals are presented in Table 1. A hundred and twenty six (31,90%) out of 395 animals were infected by Gasterophilus sp. larvae. Of the overall animals infected, males were more parasitised than females, both in relation to the total of males (34,57%) as well as the total of positive animals (66,66%).

The infection by species and region (mesoregion, Figure 2) of the Rio Grande do Sul State is presented in Table 2. Findings showed 100 (77,34%) horses infected by G nasalis and 47 (48,44%) horses infected by G intestinalis. Of the animals presenting the disease, 107 (83,59%) were suffering the infection of only one species, and 21 (16,41%) presented larvae of both species.

A total of 1.451 larvae of second and third instars was collected, with a mean of 10,97 larvae per animal. Of the total larvae found, 760 (52,38%) were of G nasalis and 691 (47,62%), of G intestinalis.

Horses infected by gasterophilids were found in all the mesoregions of the State of Rio Grade do Sul (Table 3). The infection of horses by G nasalis was identified in 24 municipalities, and the infection by G intestinalis was found in 19 municipalities.

The necropsy of the animals revealed that most were infected with up to 20 larvae (table 4). Of the 100 animals infected by G. nasalis, 1 presented larvae in the stomach, and from the 47 presenting G intestinalis, none presented larvae in the duodenum. In all the other animals the two species of gasterophilids were found on their usual anatomic fixation sites.

DISCUSSION

The results of this study show that, G nasalis is not the only species of the Gastevophilus genus acclimatised in Brazil. Differing from former studies91013"15 this work shows that G. intestinalis has definitely established in Brazil. This was confirmed by the presence of the parasite in different municipalities of the whole state, and in Rio Grande do Sul born horses.

The great prevalence of the infection by G. nasalis both in relation to the G intestinalis, as well as the number of infected animals and the number ofcollected larvae, can indicate a process of adaptation of the later species. In Italy it was found a predominance of G. intestinalis (95,2%) over G nasalis (44,8%)1. These results were similar to the ones previously found in the State of Victoria, southeast Australia17, where the infections were 81% by G intestinalis and 29% by G. nasalis. The predominance of G. intestinalis, can be related to the preference of this parasite for the stomach, favouring its access to food, and increasing its biotic potential1.

Gastevophilus intestinalis has a worldwide distribution, with a greater number of reports in temperate regions of central Europe, and south-southeast United States, and increasing in periods of lower temperatures in Europe1, Australia17 and Jordan18.

The climatic situation of the State of Victoria, in Australia, is similar to that of Rio Grande do Sul, with humid winters and temperatures lower than the national average, period of increased G. intestinalis occurrence17. In Chile the first evidences of G intestinalis was registered in the VIII region (Biobio)19, by the identification of eggs of this parasite in the hairs around the horses' mouth, and that the occurrence of this species is grater in winter. Thus, considering the biological and geographic aspects commented above, G intestinalis has potential to become the most prevalent species of the genus in Rio Grande do Sul, and move on to the other states, especially those that have an annual mean temperature lower than Brazilian's one.

Apart from the difference in the prevalence of both species, the parasitism by G intestinalis is worrisome from the clinical point of view, as there are many reports of severe digestive complications caused by this parasite20-22.

Further studies are being conducted to describe the ecology of these parasites, and monitor their occurrence in other Brazilian states or South American countries. However, the authors suggest that immediate preventive measures be taken to control the advance of the introduced species in Brazil.